1. Technical Field
The present invention relates to a gasification process and system using a dryer integrated with a water-gas-shift catalyst. More particularly, the present invention relates to a process and system for gasification, wherein a dryer integrated with a water-gas-shift catalyst is disposed in front of a gasifier at the time of using a water-containing carbonaceous feedstock to produce steam, so the steam produced from the dryer can be used to increase the production of hydrogen, and the production of synthesis gas to a feedstock can be maximized. This application claims the benefit of priority No. KR 2012-0143677 filed on Dec. 11, 2012.
2. Description of the Related Art
Generally, a gasification process is a series of processes for converting a carbonaceous feedstock such as coal, biomass or the like into synthesis gas containing hydrogen and carbon monoxide as major components using a gasification reaction under the supply of a gasifying agent (for example, oxygen, vapor, carbon dioxide or a mixture thereof). In this case, the term “synthesis gas” means artificially-made gas, not naturally-occurring gas, in a wide sense, and means a gas mixture including CO and H2 in a narrow sense. Examples of typical reaction mechanisms of such a gasification process are represented by the following Reaction Formulae 1 to 3.C+½O2→CO (partial oxidation)  [Reaction Formula 1]C+H2O→CO+H2 (steam reforming)  [Reaction Formula 2]C+CO2→2CO (carbon dioxide reforming)  [Reaction Formula 3]
Recently, a gasification process has been diversified into various kinds of technologies for producing various compounds, and application fields thereof have spread in order to produce various products including electric power. Specifically, it is known that a gasification process can be applied to power generation, ammonia preparation, oil refining and the like using hydrogen included in synthesis gas which is a main product of a gasification process; that it can be used to produce diesel oil, jet oil, lubricant base oil, naphtha and the like using synthesis gas as a feedstock of Fischer-Tropsch reaction represented by the following Reaction Formula 4; and that it can be to used to produce high value-added chemical materials such as acetic acid, olefin, dimethyl ether, aldehyde, fuel, additives and the like using methanol prepared from synthesis gas as represented by the following Reaction Formula 5. In relation to this gasification process, in the case of Fischer-Tropsch process and methanol synthesis process, it is preferred that the ratio of carbon monoxide to hydrogen be about 1:2.nCO+2nH2→CnH2n+nH2O  [Reaction Formula 4]CO+2H2→CH3OH  [Reaction Formula 5]
However, in the case of synthesis gas obtained by the steam reforming reaction represented by Reaction Formula 2 above and the carbon dioxide reforming reaction represented by Reaction Formula 3 above, the ratio of carbon monoxide to hydrogen does not reach 1:2. Therefore, generally, the ratio of carbon monoxide to hydrogen may be adjusted to about 1:2 by performing the water-gas-shift reaction of a reaction product obtained after a steam reforming reaction, a partial oxidation reaction and/or a carbon monoxide reforming reaction or by additionally supplying hydrogen to the reaction productCO+H2O→CO2+H2  [Reaction Formula 6]
Meanwhile, since coal, which a typical feedstock in a gasification process, is distributed in large quantities over a wide area throughout the world, it is attracting considerable attention again as a fuel source that can replace generally-used petroleum at the present time. Further, since biomass, which has recently attracted attention, can also be converted into a basic fraction of various kinds of fuels and platform compounds by various treatment processes, there is known a technology of applying biomass to a feedstock in a gasification reaction.
However, the above-mentioned feedstock in a gasification process contains a large amount of water. For example, coals are classified into high-grade coal and low-grade coal depending on the properties thereof, such as heating value, water content, impurities, etc. Here, it is known that the amount of low-grade coal (brown coal, etc.) reserves occupies about 45% of the total amount of coal reserves throughout the world. Particularly, when the content of water in coal is high, the coal becomes poor in terms of storability, treatability, freight and the like, so a large amount of energy is consumed to remove water from the coal prior to a gasification reaction.
In relation to this, U.S. Pat. Nos. 5,695,532 and 5,685,138 disclose technologies for using the heat of synthesis gas to dry a water-containing carbonaceous feedstock by disposing a dryer in front of a gasification reactor and recycling the high-temperature synthesis gas generated from the gasification reactor into the dryer.
However, the above-mentioned technologies do not realize advantages other than the effect of the thermal energy in high-temperature synthesis gas being used to dry a water -containing carbonaceous feedstock. Therefore, it is required to develop a gasification process that can realize additional advantages.